A novel preparation, the cardiac ganglion in the mudpuppy, is described in which it is possible to investigate mechanisms of synaptic transmission in single nerve cells. The salient features of this ganglion are (1) that the tissue is very thin and individual ganglion cells, their processes, and the synapses can be seen in the living isolated preparation and (2) there are multiple sources of synaptic input onto single neurons, including cholinergic, adrenergic, and electrical synapses. Microelectrodes can be manipulated under direct visual control in order to investigate individual ganglion cells and to probe selected parts of the neuron, such as the regions of innervation. The objective of the research is to examine how information from different sources is intergrated by nerve cells to generate a response and to study what long-term influence disuse or destruction of one type of synapse may have upon the function and structure of other synapses on the cell. In particular, I propose to investigate in detail the adrenergic synaptic mechanisms and their influence upon cholinergic transmission within the ganglion as well as how denervation or disuse of cholinergic synapses alters the properties of the remaining inputs. These results will be important not only for an understanding of how the cardiac ganglion regulates the heart rate in vertebrates, but can contribute fundamental information relating to how synapses in the central nervous system function.